Haptoglobin is an acute phase protein. It is produced by the liver and secreted into the plasma where it binds alpha-beta dimers of hemoglobin (Hamaguchi et al. 1971, Nagel and Gibson 1971, Tsapis et al. 1978, reviewed in Chiabrando et al. 2011). Haptoglobin monomers contain alpha and beta chains cleaved from a single proprotein and bonded by cystine disulfide bonds. The monomers further associate into dimers by disulfide-bonding and beta strand swapping (Andersen et al. 2012). Each haptoglobin dimer can bind two hemoglobin dimers, each containing hemoglobin alpha and hemoglobin beta.